1. Field of the Invention
The present invention relates to control systems in series with external loads and an external source or sources of electricity so as to energize and de-energize the external loads with the external source or sources of electricity depending upon the combinatorial values of a plurality of sensed parameters.
2. Description of the Prior Art
Although there are several prior art patents that disclose the use of electronic switches to effectively complete the connection of an external load to an external source of electricity, none of the prior art patents disclose a control system for sensing the combination of a plurality of external parameters and to thereby control energization and de-energization of the load in response to this combination of parameters by a control system in series with the external load and the external source of electricity. Thus, in U.S. Pat. No. 3,558,996, Mitchell, a circuit is disclosed in which a silicon controlled rectifier shorts out a full-wave bridge but which does not sense external parameters. U.S. Pat. Nos. 3,597,662, Gary, and 3,584,263, Thompson, also use a thyristor to energize an external device but do not disclose the use of remote sensors and control circuitry to energize a thyristor upon the external parameters reaching predetermined levels. Similarly, U.S. Pat. No. 3,553,535, Weber, does not teach the use of control circuitry to drive an electronic switch in response to externally sensed conditions.
Although some U.S. patents disclose the electrical shorting of a full-wave rectifier bridge by a silicon controlled rectifier, none of these U.S. Patents disclose a control system in series with an external source of electricity and external loads so as to control the energization and de-energization of each load in response to a selected combination of a plurality of external sensed parameters. Thus, U.S. Pat. No. 3,818,247, Chambers et al, discloses the use of a silicon controlled rectifier to control a load in response to a sensed condition, but the device is not in series with an external source of electricity. U.S. Pat. No. 3,818,183, Masson, discloses an electronic temperature control system utilizing an electronic switch but the disclosed system only senses one parameter, temperature. U.S. Pat. Nos. 3,708,738, Crawford et al, 3,691,404, Sweigert, Jr., 3,629,681, Gurwicz, 3,486,105, Breniere, 3,440,517, Page et al, 3,392,626, Miller et al, 3,365,654, Vollrath, 3,231,812, Paley 3,331,013, Cunningham, and 3,146,392, Sylvan, all disclose electronic circuits utilizing a fullwave rectifier bridge and the effective shorting out of this bridge by an electronic switch, but none of these patents disclose the use of external sensors to control the operation of the electronic switch so as to activate the external load. U.S. Pat. No. 3,336,524, Healey also utilizes a full-wave bridge but this bridge is not in series with the source of electricity, and the electronic switches do not operate by sensing external parameters.
Although U.S. Pat. No. 3,365,654, Johnston discloses a fullwave bridge to control activation of a load in series with a source of electricity in response to an external sensor, only one sensor is disclosed and, in addition, the circuit is used for controlling the mean electrical power fed to a load rather than its activation or deactivation. Furthermore, Johnston utilizes an external oscillator for a portion of its control circuitry which incorporates a temperature sensing resistor. Thus, this portion of the control circuitry is not in series with the source of external electricity and the external load as is the present invention.
U.S. Pat. No. 3,783,368, Dosch et al, also discloses a control system in series with a source of external electricity and an external load so as to control the power to the external load. This patent discloses the use of a single sensor so as to control the average power to the external load. The use of a hysteresis effect for activation of the load is not disclosed and indeed, the purpose for the activation of the load is for controlling the duty cycle of the load. The present invention is not concerned with the varying duty cycle of external loads but their activation in response to the combinatorial value of a plurality of externally sensed parameters. The activation of external loads by the present invention is thus used to control external devices such as furnaces and air conditioning systems so as to maintain the furnace or air conditioning system in operation until the external load is de-energized. Thus, the present invention is an on-off type of controller, rather than a proportional type controller disclosed in Dosch et al.